The absorption spectra of solutions of cobalt chloride, cobalt bromide, and cobalt iodide in concentrated hydrochloric, hydrobromic, and hydriodic acids

Abstract

In a recent paper by one of us (W. R. B) the selective absorption in the region of 600 to 710 mμ of cobalt chloride dissolved in concentrated hydrochloric acid was shown to consist of a number of superimposed, similarly shaped absorption bands. The frequency values at which these component bands exhibited a maximum of absorption corresponded with integral multiples of a common of fundamental frequency. The analysis of the observed absorption curve has now been extended into the blue so as to cover the whole of the selective absorption occurring in the visible portion of the spectrum. Similar analyses have also been obtained for the absorption shown by cobalt bromide when dissolved in concentrated hydrobromic acid and cobalt iodide dissolved in concentrated hydriodic acid. Apparatus and Method of Observation . The apparatus previously described was again used. Since the principal absorption band of cobalt bromide, as compared with that of cobalt chloride, is situated farther towards the red end of the visible spectrum, where the dispersion of the apparatus is smaller, the wave-length interval between the different sets of observations was increased from 2 to 2·5 mμ in the region of 625 to 725 mμ . At every wave-length value for which absorption measurements were obtained on the principal band, a minimum of 20 observations were made, and in the extreme red, where the sensitivity of the eye is poor, the number of observations was even larger. The average deviation from the mean absorption value E (where E = log 10 I 0 /I, I 0 being the intensity of the radiant energy passing through the comparison cell filled with the solvent, and I the intensity of the radiant energy passing through the cell containing the solvent and the material under observations) was approximately the same as in the earlier work on cobalt chloride, i. e. , 0·025.